Manufacture of flexible sheet material



March 14, 1944- R. G. TRITSMANS ,ET AL 2,344,432

MANUFACTURE OF FLEXIBLE SHEET MATERIAL Filed Nov. 15', 1939 H 2 3 a... W

omTw 52min .5 Law mw l VENTORS ATTORNEYS Patented Mar. 14, 1944 MANUFAGIURE OI FLEXIBLE SHEET MATERIAL Remi Gustave Trit smans and Serge Hendricx, Mortsel, near Antwerp, Belgium; vested in the Alien.Property Custodian Application November 15, 1939, Serial No. 304,632

In Great Britain November 25, 1938 2 Claims.

The method usually adopted for producing film stock involves the deposition onto an endless band or othersupport of a layerof this solution of the ester and the evaporation of the solvent under the action of heat, for instance by passing heated airover the layer.

In the known methods this heated air is conducted in such a way that it flows over the whole upper surface of the solution deposited on the support. This heated air must be constantly kept at a' temperature below the boiling point of the solvent; otherwise bubbles will be produced during the evaporation of the solvent, which will render the film nonhomogeneous and unsuitable for photographic purposes. This limitation of temperature has the result that the production cannot be carried out with the desired speed, which is an economic drawback.

It is further known that a film must have a certain degree of flexibility, otherwise it does not satisfy all the requirements of for instance a sup port for photographic material. For. the purpose of obtaining this required flexibility, to the solution of cellulose esters, bodies are added which may function as softening agents; however the addition of these bodies has the disadvantage of diminishing the tensile strength of the film,-

The invention helps to diminish appreciably the mentioned disadvantages of the known methods of producing flexible photographic carriers.

We have found that in producing films from.

solutions of cellulose-esters in volatile organic solvents, with or without softening agents, unexpectedly favourable results are obtained, if in ad'- dition to the heating of the space on one side, in the case of horizontally extending layers above the solution layer, to a temperature lower than the boiling point of the solvent, the space on the other side in horizontally extending layers immediately beneath the layer is heated to a temperature appreciably higher than the boiling point.

It is surprising that, although the temperature beneath the layer is higher than the boiling point, the evaporation of the solvents takes place without forming bubbles in the layer; due to this high temperature the evaporation of the solvents takes place at a quicker rate and it is possible to increase the speed of the production of the fllm without endangering its homogeneity.

It is also surprising that the film produced by the new method possesses a greater flexibility than by the known methods. It follows that the desired flexibility of the film can be obtained with less softening agents and that consequently the tensile strength can be augmented.

The invention therefore comprises the method of forming flexible films from cellulose-ester compositions, which includes the deposition, on a suitable support, for instance a, flexible band, of a solution of such ester in a volatile organic solvent, with or without the addition of softening agent, supplying to the deposited layer heat, at one side as a rule the upper side at a temperature below the boiling point of the solvent and at the other side at a temperature appreciably higher than the boiling point.

For supplying heat to the space above the layer of solution, a continuous current of heated air may be conducted past and in contact with the layer. For supplying heat to the space on the other (bottom) side, various types of heating bodies may be used as for instance an arrangement of tubes through which steam or a heated fluid is passed, or rollers which are in contact with the support, on which the layer is deposited, and are therefore kept in movement, or electric heating means.

In the drawing afllxed to this specification and forming part thereof an embodiment of our invention is illustrated by way of example in an altogether diagrammatic manner-and in which Fig. 1 is a side elevation partly in section showing equipment for carrying out the invention and Fig. 2 is a vertical cross-section thereof on the line 11-11 of Fig. 1.

In the drawing l is a tank containing the solution to be poured, for instance a solution of collodion or cellulose acetate or butyrate in acetone, methylene chloride or the like. 2 is a pipe leading to a spreading nozzle 3 arranged to pour the solution on the endless band carrier l which is supported by the two drums 5, while its longitudinal edges slide on lateral supports 8. A current of warm air entering through pipe 1 travels along the endless band surrounded by a wooden hood 8, the air escaping through pipe 9. III are heating pipes traversed by steam or the like and located near the free inner surface of the endless carrier, which is thus heated on the inner side.

The hot air traveling in a direction counter to that of the film ll spread on the carrier helps to vaporize the solvent which is gradually driven by diffusion from the part of the film contacting the carrier to the free surface contacted by the air current.

The following particulars are given by way of example for the purpose of comparing the results obtained in treating particular solutions of cellu-. lose esters by applying heat to the upper side of a horizontally extending film only, and by proceeding in accordance with the invention, that is to say by subjecting the deposited layer to heat at the upper side of the film at a temperature below the boiling point of the-solvent and also at the bottom side, but here at a temperature appreciably higher than the boiling point of the solvent.

Example 1 Cellulose diacetate was dissolved in acetone (boiling point 56) and the solution deposited in a thin layer on an endless support. The air above the layer was heated to a maximum temperature of 45 C. for the purpose of avoiding the formation of bubbles due to boiling of the solvent. The film which was obtained in this manner had a tensile strength of 7.5 kg. per mm and an elongation of only 27.7%. 1

When, however, in accordance with the invention, the air above the layer was heated to the temperature above indicated, but the space beheath the layer and its support was heated to 80 C. film obtained showed an elongation of 33.2%, the tensile strength remaining unchanged.

Eacample 2 Cellulose triacetate was dissolved in 90 parts methylene chloride (boiling point. 40) and parts alcohol. While the solution was poured the air above it was heated to a maximum temperature of 38 C. The resulting film had a tensile strength of 9.5 kg. and an elongation of 16.6%.

When, however, in accordance with the invention, the space beneath the layer was in addition heated to 90 C. the film obtained showed an elongation of 25%, the tensile strength remaining unchanged.

Example 3 Cellulose aceto-butyrate was dissolved in 90 parts methylene chloride and 10 parts alcohol and the solution poured-onto a travelling belt. The air above the layer'was heated to a maximum temperature of 38 C. To obtain-the required dryness of the film when stripping it from the support, the speed of the support could not be increased above about 1 metre per minute.

In contradistinction thereto when, in accordance with the invention, th space beneath the support was in addition heated to C. the speed of travel of th support could be raised to 1.5 metres per minute to secure the same dryness when removing or stripping the film, from the carrier.

Various changes may be made in the details disclosed in the foregoing specification without departing from the invention or sacrificing the advantages thereof.

We claim:

1. The method of forming flexible films for light-sensitive materials which comprises spreading a solution of a transparent film-forming compound in a volatile organic solvent into a thin layer and applying heat simultaneously on both surfaces of that layer, however keeping the temperature at one surface below, while raising the temperature at the other surface above the boiling point of the solvent.

2. The method of forming flexible films for light-sensitive materials which comprises spreading a solution of a transparent film-forming compound in a volatile organic solvent into a substantially horizontal thin layer and applying heat simultaneously on both surfaces of that layer, however raising the temperature at the bottom surface above, while keeping the temperature at the top surface below the boiling point of the solvent. 1

REMI GUSTAVE TRITSMANS. SERGE HENDRICX. 

